Reland "Don't refcount tracking id -> slot id mapping."

Reland "Don't refcount tracking id -> slot id mapping."

Previously we tried to refcount the tracking id to slot id mapping.
This broke in some circumstances where the number of press events was
not equal to the number of release events.

This patch switches to marking some touch events such that they don't
modify the mapping, simplifying logic, and fixing a nasty bug.

Initially landed here:
https://codereview.chromium.org/785753002/

Reverted here:
https://codereview.chromium.org/869433007/
due to memory failures.

BUG=439051
TEST=EventsXTest.TouchEventNotRemovingFromNativeMapping

Committed: https://crrev.com/211211ea4a842a8fa27660a915ae23970ef0c63c
Cr-Commit-Position: refs/heads/master@{#314327}

[tdresser, 2015-01-29 20:33:36]

tdresser@chromium.org changed reviewers:
+ sadrul@chromium.org

[tdresser, 2015-01-29 20:33:36]

I've fixed the uninitialized memory issue. I must have been asleep while
performing a manual merge...

I had removed a bunch of necessary initializers...

All changes can be seen by diff'ing patch sets 1 and 2.

[jdduke (slow), 2015-02-03 00:26:04]

On 2015/01/29 20:33:36, tdresser wrote:
> I've fixed the uninitialized memory issue. I must have been asleep while
> performing a manual merge...
> 
> I had removed a bunch of necessary initializers...
> 
> All changes can be seen by diff'ing patch sets 1 and 2.

Oh, didn't see this change, nevermind the comment on the reverted patch =/.

[sadrul, 2015-02-03 01:14:48]

lgtm

[tdresser, 2015-02-03 13:48:07]

The CQ bit was checked by tdresser@chromium.org

[commit-bot: I haz the power, 2015-02-03 13:48:50]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/886593004/20001

[commit-bot: I haz the power, 2015-02-03 13:52:04]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-02-03 13:53:08]

Patchset 2 (id:??) landed as
https://crrev.com/211211ea4a842a8fa27660a915ae23970ef0c63c
Cr-Commit-Position: refs/heads/master@{#314327}